Silicone grease and method of preparation



PatentedAug.'3,1948

SILICONE GREASE AND' METHOD OF PREPARATION George M. Hain, United StatesNavy, and William A. Zisman, Washington, Dec.

No Drawing. Application June 21, 1945, Serial No. 600,777

Claims. (Cl. 25242.1)

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3700. G. 757) This invention relates to lubricating compositions and to amethod for their preparation.

The trend in modern developments in machine manufacture, particularlyelectric motor manufacture, and the demands placed on power generatingdevices by military applications call for constant reduction in the sizeof the power unit. It is; quite possible, by appropriately insulatingthe coils in an electric motor with high temperatureinsulatingmaterials, to reduce the size of the frame of an electric motor bysubinvention to provide lubricating compositions of such stability andlubricating quality that they can be used in bearings operating at highloads and speeds and at temperatures considerably higher than thoseordinarily encountered in bearings without danger of failure of thelubri: cents or seizure of the bearings.

High-speed high-temperature bearings not only place exactingrequirements upon the periormance of the lubricant, but are also subjectto serious wear as a natural consequence of the severe operatingconditions and load placed upon them. Hence, it is another object of ourinvention to provide special lubricating compositions stable at hightemperature and especially well adapted to employment on heavy dutybearings which compositions will provide for operation of the bearingswith a minimum amount of wear.

It is another object of our invention to provide novelcorrosion-protective, stable grease compositions for employment aslubricants in bearings of electrical and mechanically driven powerunits.

It is still another object of our invention to provide a method ofpreparing the very stable lubricating composition of our invention.

Other objects and advantages of the invention will be in part obviousand in part appear hereinafter in the detailed description of thecompositions and the methods of their preparation.-

The invention, accordingly, comprises the lubricating compositions orgreases having the properties and the relation of components which willbe exemplified in the compositions hereinafter described and the methodof preparing such compositions which method of preparation involves theseveral steps and relation of one or more of such steps with respect toeach of the others thereof and will be exemplified in detail in theprocesses hereinafter described and illustrated, and the scope of theinvention will be indicated in the claims.

One class of organo-silicon compounds is illustrated by polymericcompositions of the following general structure:

in which, R, R1, R2, R3, R4 and R5 represent any alkyl, aryl, alkaryl orarallq l radicals, which compounds are available in the form of more orless viscous, oil-like fluids and, in general, are water-white andcharacterized by such properties as great thermal stability and highviscosity index. Relatively common compounds of this type are dimethylsilicone, diethyl silicone, ethyl methyl silicone, di-phenyl silicone,di-tolyl silicone, phenyl tolyl silicone, methyl phenyl silicone, ethylphenyl silicone and alkyl aryl silicone polymers. Compounds like thosenamed and methods for preparing them are described in United StatesPatents 2,352,974, 2,258,222, 2,258,219 and 2,371,068. Althoughsllicones seem to have physical properties possessed by our best mineraloils, they are not, in general, usable for purposes of lubricationbecause in many cases they do not protect the lubricated surfaces fromcorrosion and, in addition, frequently they simply do not lubricatesliding contacting metal surfaces. For example, dimethyl siliconepolymer, having a viscosity of about centistokes, one of the most commonfluids corresponding to the above general formula, has no inherent rustinhibiting valuesuch as that possessed by many hydrocarbon oils and itwill be found that it is not a boundary lubricant and seizure will occurin bearings employing it as a lubricant.

The conversion of, silicone fluids into grease compositions is hinderedby the inherent incapacity of the fluids for dissolving the soapnecessary to thicken the fluid to a grease consistency and it ispractically impossible to form a grease merely by mechanically mixingthe soap; with the fluid. We have found that by dispersing a leave agrease.

suitable alkali-metal fatty acid soap such as lithium stearate, in aconcentration of about 2 per cent in a hydrocarbon fraction ofrelatively low boiling range, for example, about 100 to 440 F., heatingthe mixture to the solvation temperature of the soap and maintaining itat substantially such temperature, a gel structure will result. At thispoint the silicone fluid, which must be one which is miscible with thehydrocarbon fraction, is added, agitated to form a homogeneous mix andthe petroleum fraction removed to The general property which thehydrocarbon fraction should have is that it be relatively low-boilingand that it be miscible with the silicone fluid to be used as the greasebase. The solvent should preferably have a boiling range well below thatof the silicone oil,,for example 100 below that of the oil and it shouldhave no heavy ends. However, the boiling range of the solvent should behigh enough to approach the solvation temperature of the soap which isgenerally close to its melting temperature. In general, hydrocarbonsolvents having boiling ranges of about 300 to 400 F. are suitable atatmospheric pressure or low boiling point solvents can be used at300-400 F. under pressure. Such hydrocarbon fractions or mutual solventsare benzene, petroleum ether, naphthas, deodorized kerosene and,generally; those hydrocarbon fractions used as insecticide carrying oilsare useful in that they have the right boiling temhaving a siliconefluid as a base can be prepared with any desired soap concentration.

The nature, scope and method of accomplishing the objects and carryingout the method of the invention will be apparent from the followingexamples describing the compositions and the method of preparing them.In the following examples all proportions are given in parts orpercentages by weight:

' Example I 1 Lithium stearate, 2 parts, was dispersed in 100 parts byweight of a petroleum fraction having a boiling range of 300 to 400 F.(100 F. flash point naphtha) and the mixture heated to about 300 andmaintained at that temperature until the lithium stearate had gone intosolution to form a thick gel. Twenty-two (22) parts by weight of phenylsilicone (Dow-Corning 700 serles) having a viscosity of about 100centistokes at 25 C. was added to the lithium soap-petroleum fractiongel at the elevated temperature and the mass'mixed to a uniformconsistency. After the entire mass had been blended to a uniformconsistency, it was held at an elevated tem- Six (6) parts of lithiumstearate were dispersed in 45 parts of petroleum ether and thedispersion heated to a temperature of 250 C. in a bomb. I At thistemperature, the pressure within the bomb was about 200 pounds persquare inch. When-solvation of the soap was complete, after about 30minutes, 24 parts of dimethyl silicone polymer (Dow-Corning 500 series),having a viscosity of centistokes at 25 C., were added to the bombwithout permitting the temperature or pressure to drop. After a 20minute period of agitation of the bomb to develop homogeneity of themixture therein, the bomb was cooled rapidly and pressure released.Substantially all the petroleum ether evaporated off and a smoothhomogeneous grease comprising about "20 per cent soap in dimethylsilicone was left.

It will be noted from this example and others to be given that very lowboiling solvents such as petroleum ethers can be used for bringing thesoap into a solvated condition. However, inasmuch as a relatively hightemperature is necessary to bring the soap into such condition, it

is necessary that the process be carried out in a pressure vesselof sometype such as a born with attendant inconvenience. v

Example III of the mixture in the bomb had developed, the I pressure wasreleased and the petroleum ether allowed to evaporate off to leavebehind a smooth homogeneous grease comprising about 15 per cent oflithium soap in dimethyl silicone.

Example IV Four (4) parts of lithium stearate were dispersed in 30 partsof Stoddard Solvent and the mixture heated to 150 C. in an open vesselto complete solvation of the soap. When a maximum thickening had beenattained, approxiperature of about 200 to 250 F. in a vessel under areduced pressure of 10 millimeters of mercury in order to assist in theremoval of the petroleum fraction. The product, upon the removal of thepetroleum fraction, was a stable grease of very smooth consistencyhaving a soap concentration of about 9 per cent. I

Balancing ingredients, such as corrosion inhibitors, can be blended withthe composition in the amount of about a few tenths to about 2 parts byweight, depending upon the severity of the corrosive condition to whichthe grease will in a current of air until all of the solvent hadevaporated before being allowed to cool.

Example V Three (3) parts of lithium stearate were dispersed in 35 partsof deodorized kerosene (boiling range 425-475 F.) and the mixture heatedto 250 C. to effect solvation of the soap therein. Upon the formation ofa thick gel, there were eflect solvation of the soap.

mixture held at 250 C. and agitated until a homogeneous mass was formed.The mass was then poured into a shallow pan, held at about 150 C. untilsubstantially all of the solvent had evaporated oil and allowed to cool.

Example VI with the result that a very thick gel was left in the vessel.At this stage 20 parts of diethyl and dimethyl silicone polymer (1-1 byweight) were added and the total mixture agitated and held at 150 C.until a completely homogeneous mix was formed. The mix was then pouredinto a shallow pan and held at a temperature of about 125 C. in acurrent of warm air until all of the solvent had been removed before itwas allowed to cool.

Example VII Lithium stearate, 6 parts, was dispersed in about 200 partsby weight of a petroleum traction having a boiling range of 300 to 400F. (100 flash naphtha) and the mixture heated to about 300 andmaintained at that temperature until the lithium stearate had gone intosolution to form a thickened gel. As pointed out in connection withother examples, the completion 01' this stage is identifiable as thepoint at which maximum thickening of the solution occurs. Fortytwo (42)parts by weight of a mixture of phenyl silicone polymer and ethylsilicone polymer (approximately 1-1 by weight) were added to the gelafter evaporating off from the gel part of the solvent used forsolvating the soap. The

residual soap gel and the silicone polymer were mixed at about 300 F. toa uniform consistency. The product, upon removalof the rest of thepetroleum fraction, was a grease of very smooth consistency which had asoap concentration of about 12 per cent.

The compositions of these examples thus contemplate using more than 70parts of the silicone polymer blended with less than 30 parts of thelithium stearate.

Thus the method of preparing. silicone-base grease compositions inaccordance with the invention comprises blending a soap with thesilicone fluid by employing a relatively low-boiling petroleum orhydrocarbon fraction as a mutual solvent for bringing the soap intocolloidal solution in the base fluid. From the above examples it can beseen that the mutual solvent used for solvating the soap in aid ofbringing it into colloidal dispersion within the silicone fluid shouldbe one which has a relatively narrow boiling range, preferably amoderately high boiling point which, however, is about 100 below that ofthe silicone fluid being used and further it should have no heavy ends.The examples also show that the solvent can be removed to a substantialextent prior to the addition of the silicone fluid. It is essential incarrying out the method that the silicone fluid used as a base for thegrease be compatible with the petroleum fraction 6 l i and that thelatter has no heavy ends. some speciflccompositions of silicone greaseswhich can be prepared according to the method of our invention aresuggested in the following table:-

Soap I Silicone Lithium stearate diphenyl silicone Do. dimetbyl siliconeDo. dietbyl silicone Do. halogenated alkyl or aryl silicone All thegrease compositions prepared according to the above examples werecharacterized by extreme stability. Tests showed that bleeding of thegreases was, in all cases, less than 4 per cent. After 3 hours atambient temperatures in a BEC grease testing machine running on a 5-gram sample the microcone penetration changed only from 89 to 93 (thetest is described by Kaufman et al., in Ind. Eng. Chem., Anal. Ed., 11,108

(1939) Worked samples of this type showed no tendency to bleed afterstanding for four months. 7

Another test involving operation in a Fafnir 305W unshielded bearing at1750 revolutions per minute under a load of 750 pounds per square inchfor 123 hours showed that the greases developed no evidence of roughnessand were adherent and stable to working loads.

Since certain changes may be made in the compositions of our inventionand changes made in the methodof their preparation and differentembodiments of the invention can be made by varying the fluid used asthe base. the soap and the balancing ingredients, it is intended thatall matter contained in the above description and examples shall beinterpreted as illustrative and descriptive of a few preferredembodiments and not in a limiting sense.

"Consisting essentially of" as used in the claims means that thecomposition is made up almost entirely of the ingredients recited andthese ingredients are the main and characterizin ones, but thisexpression does not exclude the presence of minor amounts of otheringredients which are commonly employed in lubricating compositions orwhich are merely inert. Such added ingredients would not change theessential character of the composition.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

Having described our invention what we claim as new and desire to secureby Letters Patent of the United States is:

1. A lubricant consisting essentially of, an organo-silicon polymer as abase fluid blended with a minor amount of lithium stearate to produce astable grease.

2. A lubricating composition consisting essentially of. as a base fluid,more than 70 parts of an alkyl silicone polymer having a viscosity ofabout centistokes at 26 C. blended with less than 30 parts of lithiumstearate to produce a stable grease.

3. A lubricating composition consisting essentially of, as a base fluid.more than 70 parts of an aryl silicone polymer having a viscosity ofabout 100 centistokes at 25 C. blended. with less than 30 parts oflithium stearate to produce a stable grease.

4. A lubricating composition consisting essentially of, as a base fluid,more than 70 parts of a mixed alkyl-aryl silicone polymer having aviscosity of aboutlOO centistokes at 25 C. blended with less than 30parts of lithium's'tearate to produce a stable grease.

5. A lubricating composition consisting essentially of. as a base fluid,about 85 parts of dimethyl silicone having a viscosity of about 100centistokes at 25 C. blended with about 15 parts of lithium stearate toproduce a stable grease.

6. A lubricating composition consisting essentially of, as a base fluid,about 85 parts of diphenyl silicone polymer having a viscosity of about100 centistoks at 25 C. blended with about 15 parts of lithium stearateto produce a stable grease.

7. The method of preparing a silicone-base grease consisting essentiallyof, dispersing lithium stearate in a relatively low-boiling petroleumfraction, heating said dispersion of lithium stearate to inducesolvation, adding to the solution thus obtained a silicone fluidmiscible with said petroleum fraction, maintaining said mixture at anelevated temperature until homogeneity of the mixture is attained, andremoving the petroleum fraction by evaporation to leave a residue of astable grease consisting essentially of the lithium stearate dispersedin the silicone base fluid.

8. The method of preparing a silicone-base grease, dispersing lithiumstearate in a relatively large amount of a petroleum fraction, heatingsaid dispersion to an elevated temperature to form a relatively dilutesolution thereof, adding to said solution a silicone fluid miscible withsaid petroleum fraction, maintaining the mixture at an elevatedtemperature until homogeneity is attained, and removing the petroleumfraction to leave behind as a residue a stable grease consistingessentially of a gel of the lithium stearate in the silicone base fluid.

9. The method of preparing a silicone-base grease consisting essentiallyof, dispersing about 2 parts of lithium stearate in about 100parts of apetroleum fraction which boils in the range of about 200 to 400 F.,heating said dispersion of lithium stearate in said petroleum fractionto about 300 F. to produce solvation of the lithium stearate therein toform a solution of about 2 per cent concentration, adding to thesolution thus obtained about 20 parts of a silicone fluid which ismiscible with said petroleum fraction, maintaining said mixture at about'solvation temperature until homogeneity is attained, and removing thepetroleum fraction by evaporation to leave a residue of a stable greasecontaining about 12 per cent of lithium stearate dispersed, in thesilicone base fluid, I i

10. The method, of preparing a silicone base grease consistingessentially of, dispersing lithv REFERENCES CITED The followingreferences are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,753,659 Kokatnur Apr. 8, 19302,274,673 Earle Mar. 3, 1942 2,274,674 Earle Mar. 3, 1942 2,350,906Kokatnur et al. June 6, 1944 2,351,280 Morgan June 13, 1944 2,354,171Morgan July 18, 1944 2,362,767 Morgan Nov. 14, 1944 2,375,007 Larsen May1, 1945 2,407,037 Sowa -1 -1 Sept. 3, 1946 OTHER REFERENCES TheSilicones--A New Plastics Family-Article in Plastics, Jan. 19455 pages.

Dow-Corning Plug Cock Grease-4 pages-pub. by Dow-Corning Corp. ofMidland, Michigan.

5 Received in Patent Ofiice March 12, 1945.

Dow-Corning Fluids-8 pages-pub. by Dow- Corning Corp. of Midland,Michigan. Received in Patent Oflice Feb. 17, 1945.

Dow-Corning Silicones4 pagespub. by Dow- Corning Corp. of Midland,Michigan. Receive in Patent Office Mar. 12, 1945.

